Wider utility of high-pressure discharge lamps having a metal halide fill can be obtained by decreasing the power input to the lamps, so that the field of use can be extended. Lamps of this type can then also be used for home, office, and other work-place illumination. The lamps should be compatible with existing supply networks and must have particularly desirable firing or ignition as well as operating characteristics, compatible with replacement of ordinary incandescent or fluorescent lamps in illumination circuits.
U.S. Pat. No. 4,199,701, BHATTACHARYA, (assigned General Electric) described a metal halide, high-pressure lamp located within an exterior vessel or bulb, in which a miniaturized discharge vessel or bulb, that is, having a volume of less than 1 cm.sup.3, is used. The electrodes are introduced through respective opposite ends of the discharge vessel--so that it will be a double-ended bulb--being melted through press ends of the discharge vessel. The discharge vessel is held by a support structure which is carried at the press stem secured to a contact base, for example of the screw-in type, and which also supports the outer envelope of the lamp.
In order to obtain desirable ignition and operating characteristics, a penning mixture of neon admixed with argon, crypton or xenon is used. To decrease loss of neon by diffusion from the arc tube or actual discharge vessel, the outer bulb retains a neon filling.
Metal halide high-pressure discharge lamps of low power are also described in the referenced U.S. Pat. No. 4,321,504, KEEFFE et al (assigned GTE Products Corp.) and have a single-ended arc tube or discharge vessel in which two electrodes are melted through a single press stem. There is no disclosure relating to an outer envelope or bulb in this structure. To obtain desirable increase in the lifetime of the lamp, the distance between the electrodes and the adjacent surfaces of the arc tube should have a certain dimension, as described.